This invention relates generally to flat panel display devices and particularly to a modulator structure for such devices and to a method of making such structure.
Prior art flat panel display devices, such as those described in U.S. Pat. Nos. 4,316,118 and 4,199,705, both to C. H. Anderson et al. include a baseplate and a faceplate which are held in a spaced parallel relationship by a plurality of external side walls. A phosphor screen is arranged on the faceplate to produce the desired image when struck by electrons. The envelope is divided into a plurality of channels by internal walls which provide support against collapse due to atmospheric pressure. Each of the channels includes a guide mesh structure along which electron beams propagate the lengths of the channels until one line of the visual display is to be produced. The electrons are emitted from a cathode which is arranged at the entrance to each guide mesh structure. Pairs of modulation electrodes overlap the cathodes so that each electron beam can be individually modulated to produce the desired image on the screen. Interaction of the modulation voltages on adjacent pairs of modulation electrodes is avoided by the use of isolation electrodes between the modulation electrodes. The isolation electrodes are all biased at the same constant voltage. The constant electric field produced by the isolation electrodes prevent the varying electric fields of the modulation voltages from interacting and adversely affecting the modulation of the electron beams.
Flat panel display devices built in accordance with the prior art operate satisfactorily for the purposes intended. However, difficulties sometimes arise because it is essential that the modulation electrodes in each pair are electrically connected. In the device of U.S. Pat. No. 4,199,705, for example, the modulation electrodes are placed onto separate pieces and subsequently bonded together to form the electrical contact. It is possible for the bond to separate during subsequent processing or due to heat expansion during operation. Problems can also arise because electrons can charge the insulative substrate which supports the electrodes and cause the modulation and isolation electrodes to short together. It is also possible for the barium used in the getter flashing or from the cathode to short out the modulation and isolation electrodes. Additionally, the fabrication of the modulator described in U.S. Pat. No. 4,199,705 is expensive and difficult.
There, therefore, is a need for a modulator structure, and method of fabrication, which assures electrical contact of the modulator electrodes in each pair, which assures electrical separation of the modulation electrodes and the isolation electrodes and which is inexpensive to reliably fabricate. The instant invention fulfills this need by the provision of a modulator structure and method which assures the integrity of the electrical contact of the electrodes in each modulator electrode pair and by the provision of an isolation electrode which covers all exposed insulators in the cathode region.